In a :ref:`variable-type calculation <tutorial_calc_variable>`, it is possible to test if a variable is accessible (there is no :ref:`access_control` problem).
..prerequisites:: Prerequisites
- We assume that Rougail's library is :ref:`installed <installation>` on your computer.
- It is possible to retrieve the current state of the various Rougail files manipulated in this tutorial step
by checking out the corresponding tag of the `rougail-tutorials` git repository.
Each tag corresponds to a stage of progress in the tutorial.
Of course, you can also decide to copy/paste or download the tutorial files contents while following the tutorial steps.
If you want to follow this tutorial with the help of the corresponding :tutorial:`rougail-tutorials git repository <src/branch/1.1>`,
-:ref:`tutorial_domainname``address` that allow IP and hostname, this variable is accessible in type HTTP, HTTPS/SSL, SOCKS4 or SOCKS5
-:ref:`tutorial_port`, this variable is accessible in type HTTP, HTTPS/SSL, SOCKS4 or SOCKS5
-:ref:`tutorial_web_address` URL, this variable is accessible in type PAC URL or WPAD
..image:: images/foxyproxy.png
There is a particularity to these three variables.
We want to copy the values of the equivalent variables available in Firefox.
The reason is obvious; it simplifies data entry.
Variables are not always available. It is possible to test their presence in a :ref:`Jinja template <tutorial_jinja>`, as we have :ref:`already seen <tutorial_propertyerror>`.
But it's not the most effective. It is preferable to perform a :ref:`variable-type calculation <tutorial_calc_variable>` using the property `propertyerror` to `false`.
This property allows you to disable errors in case of :ref:`access problems <access_control>`.
As expected, calculating the default value works without issue even though the variables involved in the calculations are inaccessible.
The values are therefore `null`. These variables are not :ref:`nullable <tutorial_nullable>`, so the :ref:`overall coherence <overall_coherence>` of the :ref:`configuration` is not guaranteed.
Now try it in the :term:`read write mode` with the Rougail CLI:
:caption:The :file:`config/04/config.yml` user data
As you can see, the address and port are defined in the Firefox :ref:`namespace <tutorial_namespace>` but not in the FoxyProxy :ref:`namespace <tutorial_namespace>`.
